In a large skillet over medium heat, add the ground beef. Cook, breaking it apart with a wooden spoon, until browned (about 5-7 minutes).
Once the beef is browned, add the diced onion and minced garlic to the skillet. Sauté together until the onion is translucent (about 3-4 minutes).
Stir in the taco seasoning and add the water. Mix well and bring to a simmer. Allow it to cook for another 5 minutes, stirring occasionally, until the sauce thickens.
While the beef mixture is simmering, prepare your taco shells or warm the tortillas in a separate pan if desired.
To assemble, place a generous amount of the beef mixture into each taco shell or tortilla.
Top with shredded lettuce, diced tomatoes, shredded cheese, and sour cream. Add jalapeños and fresh cilantro if desired.
Serve immediately, and enjoy your delicious ground beef tacos!